Water is the basis of life. Every animal and every plant contains a substantial proportion of free or combined water in its body, and no kind of physiological activity is possible in which this fluid does not play an essential part. Water is, of course, necessary for animal life, while moisture in the soil is equally imperative for the life and and growth of plants and trees, though the quantity necessarily varies enormously with the species. The conservation and utilization of water is thus fundamental to human life. Apart from artesian water, the ultimate source in all cases is rain or snowfall.

520. Water is the basis of life, because

(a) it is seen everywhere on the earth

(b) itis obtained from the sea and rain

(c) it helps living things to exist

(d) it is necessary for the birth and growth of all living things

521. No kind of physiologiclal activity is possible without water, because